1. Field of the Invention
The present invention relates to orthopedic prosthetic devices and more particularly to an improved prosthesis for replacing a portion of a patient's knee joint. Even more particularly, the present invention relates to an improved tibial prosthesis that is modular, having a removable metaphyseal stem portion that includes a cylindrical section and a tapering section, and wherein parallel fins extend continuously from the proximal to the distal end of the metaphyseal stem, tracking first the cylindrically shaped section and then the tapering section.
2. General Background
A number of tibial components have been patented that relate to tibial components having a tray, and a stem portion that provides initial fixation when the prosthesis is implanted.
An example of a modular tibial support is seen in the Elias U.S. Pat. No. 5,246,459 entitled "Modular Tibial Support Pegs for the Tibial Component of a Prosthetic Knee Replacement System". The Elias Patent discloses a modular tibial support peg operable to secure a tibial component of a knee joint prothesis to a tibia having a groove. The modular tibial support peg includes a cylindrical body with a ridged outer surface operable to engage the groove in the tibia. The modular tibial support peg further includes a plurality of spikes extending inferiorly from the cylindrical body. The spikes are operable to engage the tibia at the inferior end of the groove.
U.S. Pat. No. 5,137,536 issued to Tomihisa Koshino describes a tibial component for an artificial knee joint. The tibial component includes a plate section having an upper surface and a pair of bearing surfaces parts that are adapted to be in sliding contact with a femoral component. A stem portion extends downwardly from a lower surface of the plate section. A pair of blade like members extend obliquely and posteriorly from the stem. The plate section has a lower surface with a plurality of elongated grooves for improving affinity with respect to the surrounding bone, the grooves including a first group of grooves and a second set of group of grooves extending perpendicularly to the first group of grooves.
A British Patent 2,192,543A discloses a peg for use in prosthetic devices. A peg of metal or ceramics is defined as being suitable for use as a fixator and/or a bone strengthener in connection with a prosthetic device. The peg has a portion of generally tapered form that increases in cross section from an insertion end. The surface of the tapering end portion has alternating ridges along its length extending therearound, each successive ridge as one moves away from the insertion end having an outer surface spaced by a comparatively small amount at a greater distance from the axis of the peg then the outer surface of the preceding ridge. The peg may be discrete or form a part of a prosthetic device.
U.S. Pat. No. 4,938,769 issued to James Shaw discloses an end bone anchorage assembly for a tibial prosthesis that includes an axially elongated central stem and a plurality of elongated fixation pegs spaced from the stem. The stem and the pegs have proximal and distal ends. The proximal ends of the stem define an attachment table. A plurality of structural links interconnect the pegs and the stem. Means is provided for removably attaching a tibial tray to the assembly wherein each of the pegs is connected to the stem by the structural link.
The Bolesky et al. U.S. Pat. No. 4,479,271 entitled "Prosthetic Device Adapted to Promote Bone/Tissue Ingrowth" discloses a tibial component that includes a table and at least one porous metal stem protruding from the lower base surface of the bottom base layer of the table wherein the outer surface of the protruding stem is adapted to be in direct contact with the prepared bone surface to promote the ingrowth of bone and/or tissue and wherein each of the protruding porous metal stems includes a bore therethrough which extends from the distal end of the stem through the upper surface of the bottom base layer of the table.
The Murray U.S. Pat. No. 4,016,606 discloses a knee prosthesis that includes a tibial component with a tray and with a stem adapted to be received in a longitudinal bore in the patient's femur. The stem has one end that is integral with a depending generally spheroidal surface having generally the same radius as the radius of the spheroidal depression in the insert.